IMPRIME PGG (β(1,6)-[poly-1,3)-D-glucopyranosyl]-poly-b(1,3)-D-glucopyranose, Biothera, Eagan, Minn.) is a soluble form of yeast-derived β-glucan. Laminarin is another example of a β-1,3/1,6 glucan, however laminarin is derived from algae and differs chemically from IMPRIME PGG.
Yeast β-glucans are conserved microbial structures not found in mammalian cells. IMPRIME PGG is a soluble β-glucan isolated from yeast. Since IMPRIME PGG is a conserved microbial structure not found in mammals, and IMPRIME PGG is recognized by innate immune cells, IMPRIME PGG is classified as a pathogen-associated molecular pattern (PAMP). In general, PAMPs are microbial components that are first recognized by the innate immune system resulting in immune activation.
Activation of the innate immune system with soluble β-glucans can result in anti-tumor activity in mice (Allendorf et al., 2005, J Immunol., 174(11):7050-7056; Li et al., 2006, J Immunol., 177(3):1661-1669; Salvador et al., 2008, Clinical Cancer Research, 14:1239-1247). Unlike other PAMPs (e.g., LPS, Pam3Cys, poly I:C), IMPRIME PGG does not appear to induce overt production of pro-inflammatory cytokines such as, for example, the NF-κB-regulated cytokines tumor necrosis factor-α (TNF-α) and interferons (e.g., IFN-α and IFN-γ). Thus, IMPRIME PGG may modulate immune responses in a different manner than other PAMPs.